Paul in Colosians and other letters was fighting the judiazers--men who sought to apply the most central Jewish ceremonial law--that which predates all the feasts you mention, going back to Abraham himself--onto the backs of gentile believers.
His arguments were SPECIFICALLY about Jewish ceremonial questions, like feast days, new moons and special Sabbaths...
This verse is DEFINITELY about exactly what you are talking aobut, and refutes you fully--and I think you know that--intellectuallizing to the contrary.
The Acts 15 Council of Jerusalem makes plain (explicitely repeated no less than 3 times in Acts) what the formerly pagan gentile believers were responsible to follow. Avoiding meat sacrificed to idols, eating blood, and sexual immorality. No mention of following Jewish feasts, sorry.
I just showed you scripture where Paul said specifically that he was referring to "commandments and doctrines of men", and "rudiments of the world". You have a flawed understanding of Colossians 2. It's not your fault. In man's eagerness to disobey God he wrests and twists scripture to make it fit tradition:
2Pe 3:15 and regard the patience of our Lord as salvation; just as also our beloved brother Paul, according to the wisdom given him, wrote to you,
2Pe 3:16 as also in all his letters, speaking in them of these things, in which are some things hard to understand, which the untaught and unstable distort, as they do also the rest of the Scriptures, to their own destruction.
Paul's letters, as Peter says, are NOT easy to understand. The untaught and unstable distort scripture to make it fit their desires and traditions.
Is it your position that this list is ALL that was expected of gentiles who became Christians? They could kill? They could rob? They could worship other Gods?
Clearly you're not understanding this either. This list is for starters. They were expected to learn the rest every sabbath:
Act 15:21 For Moses of old time hath in every city them that preach him, being read in the synagogues every sabbath day.